Backpack



FIG. 1 is a perspective view of a backpack according to the design;

FIG. 2 is a front view thereof;

FIG. 3 is a back view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a top view thereof; with the straps shown in a different position; and,

FIG. 7 is a bottom view thereof with the straps shown in a different position.

The broken lines depict portions of the backpack that do not form part of the claimed design. 

CLAIM The ornamental design for a backpack, as shown and described. 